MNRAS 446, 2823–2836 (2015) doi:10.1093/mnras/stu2256
Differences between CO- and calcium triplet-derived velocity dispersions in spiral galaxies: evidence for central star formation?
Rogemar A. Riffel,1‹ Luis C. Ho,2,3 Rachel Mason,4 Alberto Rodr´ıguez-Ardila,5 Lucimara Martins,6 Rogerio´ Riffel,7 Ruben Diaz,8 Luis Colina,9 Almudena Alonso-Herrero,10 Helene Flohic,11 Omaira Gonzalez Martin,12,13,14 Paulina Lira,15 Richard McDermid,4,16 Cristina Ramos Almeida,12,13 Ricardo Schiavon,2,17 Karun Thanjavur,18 Daniel Ruschel-Dutra,7,12 Claudia Winge8 and Eric Perlman19 Affiliations are listed at the end of the paper Downloaded from
Accepted 2014 October 24. Received 2014 October 24; in original form 2014 May 20
ABSTRACT http://mnras.oxfordjournals.org/ We examine the stellar velocity dispersions (σ ) of a sample of 48 galaxies, 35 of which are spirals, from the Palomar nearby galaxy survey. It is known that for ultra-luminous infrared galaxies (ULIRGs) and merger remnants, the σ derived from the near-infrared CO band heads is smaller than that measured from optical lines, while no discrepancy between these measurements is found for early-type galaxies. No such studies are available for spiral galaxies – the subject of this paper. We used cross-dispersed spectroscopic data obtained with the Gemini Near-Infrared Spectrograph, with spectral coverage from 0.85 to 2.5 µm, to obtain σ measurements from the 2.29 µm CO band heads (σ CO) and the 0.85 µm calcium triplet at Universidad de Chile on May 20, 2015 (σ CaT). For the spiral galaxies in the sample, we found that σ CO is smaller than σ CaT, with a mean fractional difference of 14.3 per cent. The best fit to the data is given by σ opt = (46.0 ± 18.1) + (0.85 ± 0.12)σ CO.This‘σ -discrepancy’ may be related to the presence of warm dust, as suggested by a slight correlation between the discrepancy and the infrared luminosity. This is consistent with studies that have found no σ -discrepancy in dust-poor early-type galaxies, and a much larger discrepancy in dusty merger remnants and ULIRGs. That σ CO is lower than σ opt may also indicate the presence of a dynamically cold stellar population component. This would agree with the spatial correspondence between low-σ CO and young/intermediate-age stellar populations that has been observed in spatially resolved spectroscopy of a handful of galaxies. Key words: galaxies: active – galaxies: kinematics and dynamics – galaxies: star formation – infrared: galaxies.
relation a very useful alternative. Cosmological simulations sug- 1 INTRODUCTION gest that the central SMBH evolves together with the host galaxy The empirical relationship between the stellar velocity dispersion and plays a fundamental role in its evolution (Di Matteo, Springel (σ ) of the spheroidal component of galaxies and the mass of the & Hernquist 2005; Springel, Di Matteo & Hernquist 2005; Bower supermassive black hole (SMBH; M•) at their centre (e.g. Fer- et al. 2006; Nemmen et al. 2007), and this co-evolution may be the rarese & Merrit 2000; Gebhardt et al. 2000) has been extensively mechanism that leads to the M•–σ relation. The intrinsic scatter used to estimate M• in active and inactive galaxies. More direct in the relation (i.e. the range of M• found for a given σ ) therefore determinations of M•, through stellar kinematics within the black contains information about the processes of galaxy and black hole hole’s sphere of influence, or broad emission line measurements, evolution (e.g. Gultekin¨ et al. 2009). Besides the M•–σ relation, are only feasible for a limited number of objects, making the M•–σ stellar velocity dispersion measurements are also relevant for many other astrophysical applications, including the galaxy Fundamental Plane (e.g. Djorgovski & Davis 1987; Dressler et al. 1987;Falcon-´ E-mail: [email protected] Barroso, Peletier & Balcells 2002;Bernardietal.2003; Gebhardt